Over excursion protection for subwoofer

[Buzzy]

Hi ! I am looking for a circuit that can prevent a subwoofer from over excursion so that it doesn't bottom out. I don't know what is the right name for this kind of circuit.

I shall also elaborate what i am trying to do here. I upgraded the driver for my SVS subwoofer i bought some time ago. So i have the old driver which is in perfect working condition. I have built an enclosure for it. The original SVS subwoofer has variable subsonic filter switch with 25Hz, 20Hz, 16Hz and bypass settings. http://www.svsound.com/products-sub-box-plus2.cfm I would like a circuit that will do the same. But i think i will not need so many. Maybe just the 20 Hz filter.
Thank you.

[GM]

It's a high pass filter (AKA subsonic filter or 'rumble' filter when spinning vinyl).

Google is your friend:
http://www.google.com/search?hl=en&c...it&btnG=Search
http://www.google.com/search?hl=en&c...er&btnG=Search

GM

[chris661]

Provided you know what the excursion looks like (on a graph, eg winISD) at the highest sound levels you will play, you can decide the frequency at which the speaker will bottom out. Remember this will be at more than Xmax, so when the excursion goes to a decent amount more than that, put the filter in.

I made a 2nd order low-pass using a variable resistor in place of the 2 resistors which determine the frequency. I presume you can do similar with a high pass, if you wanted infinite adjustability.

I would recomend setting it to around 10Hz, as putting it to 20Hz or more could affect the sound comming out.

As I said above, it depends on the box and driver you are using, as they will determine the frequency and volume at which the speaker will bottom out.

[AndrewT]

Originally posted by chris661
I would recommend setting it to around 10Hz, as putting it to 20Hz or more could affect the sound coming out.

you can't have deep bass and excursion limitation, they are mutually exclusive.
It's one or the other or compromise both.

Have a look at a 5th or 6th order Vented box that protects the driver from excessive excursion and gets deeper base than simply applying a high pass filter.

Bullock explained this well, I think Linkwitz also covers it.

[Taterworks]

I disagree heartily with that statement, having owned both subs that included a 'subsonic' filter/"rumble" filter and those that did not.

With some material containing subsonic information, there would sometimes be a visible < 10 Hz 'wobble' in the cone as frequencies that could be reproduced well by the subwoofer were riding on top of frequencies that would not be audible at *any* level, or even palpable. The effect of this 'wobble' is to simply drag the cone to various offset positions through its finite magnetic field, reducing the amount of available Xmax in one direction and causing distortion in the audible frequencies of a complex bass signal to increase as the coil actually exits the magnetic field.

The purpose of a subsonic filter, then, is to prevent the subwoofer from killing itself trying to reproduce impractically low frequencies which are not only inaudible but use up the driver cone's excursion envelope very quickly unless there's an enormous amount of radiating surface.

The subsonic filter serves another, more vital role in vented-box subwoofers. Below the enclosure's tuning frequency, the enclosure begins to 'unload' -- that is, the ports begin acting simply like holes in the box, and there is no longer any air spring to support the rear of the cone. Driving a vented sub below its tuning frequency will only result in wild excursions of the cone and very little meaningful output, particularly if the enclosure is tuned above the driver's Fs. The purpose of the SVS subwoofer's subsonic filter is to prevent driver overexcursion below box tuning due to inaudible subsonic components of the bass signal. (Using a 6th-order vented design as mentioned above instead of the more typical 4th-order alignment only increases excursion demands just above the tuning frequency, where the system behaves more like a big sealed box than a vented box. There is no free lunch.)

The alternative to a subsonic filter is to use subwoofers with acoustic-suspension alignment sealed enclosures that have a natural rolloff induced by the decreasing compliance of the driver's suspension at lower frequencies combined with the decreasing compliance of the internal air spring with decreasing frequency. However, some subwoofers with an acoustic-suspension design still employ excursion-limiting filters. In the case of Velodyne subs, which incorporate excursion limiters, the goal is to prevent distortion from increasing due to deliberately overdriving the electromechanical system, at the expense of some output capability.

To say that 'subsonic filters are for wimps' takes a very narrow view that ignores the way subwoofers behave outside of their intended passband and performance envelope, especially in light of the way that subwoofers are often abused. Subsonic filters/excursion limiters do a great deal to 'idiot-proof' a subwoofer and expand its performance envelope within its passband.

A rumble filter project: http://sound.westhost.com/project99.htm

[Buzzy]

Thanks Taterworks. The rod elliot rumble filter needs 2 opamps. Can i use a single TL02 chip which has 2 opamps in it or must i use another TL072 chip ? The yellow capacitors are they polyester film type ? I mean the C1 to C5 .

[AndrewT]

Originally posted by AndrewT
you can't have deep bass and excursion limitation, they are mutually exclusive.

Originally posted by Taterworks
I disagree heartily with that statement,

Is that the statement you disagree with?
or is this what you disagree with?

Bullock explained this well,

[Andersonix]

The word y'all are looking for is "infrasonic."

[Buzzy]

The rumble filter on Rod elliots website shows the ground from the transformer(the one powering the rumble filter) being connected to the signal ground. The amp i am using is UCD 400. The connection diagram for the amp is here http://www.hypex.nl/docs/UcD180400.pdf . I am a little worried if connecting the the rumble filter's signal ground (connected to the ground of transformer) to the amp's signal ground in, would result in any disaster.

[Chip-Audiophile]

Originally posted by Buzzy
Thanks Taterworks. The rod elliot rumble filter needs 2 opamps. Can i use a single TL02 chip which has 2 opamps in it or must i use another TL072 chip ? The yellow capacitors are they polyester film type ? I mean the C1 to C5 .

I am looking at building one of these subsonic / rumble filters too and would also like confirmation if the yellow capacitors are polyester film type or MKT capacitors.